Controller of variable valve actuator

ABSTRACT

The present invention provides a variable valve mechanism control device that is capable of reducing the power consumption and rating of an electric motor by allowing camshaft rotary inertia torque to reduce spring reaction force during a valve lift. Camshaft rotary inertia force is increased to a value not smaller than a predetermined value before the start of a valve lift. During the time interval between the instant at which the valve lift starts and the instant at which the maximum lift is provided, the spring reaction force of a valve spring is used as deceleration torque for the camshaft rotary inertia force. During the time interval between the instant at which the maximum lift is provided and the instant at which the valve lift terminates, the spring reaction force is used as acceleration torque for the camshaft rotary inertia force. The camshaft rotary inertia force cancels the spring reaction force so that motor torque generated during a valve lift is composed of counter-friction torque only.

TECHNICAL FIELD

The present invention relates to a variable valve mechanism controldevice with an electric motor, and more particularly to drive controlover an electric motor.

BACKGROUND ART

A variable valve mechanism control device with an electric motor isknown (refer, for instance, to Patent Document 1). The control devicedisclosed in Patent Document 1 includes a torque reduction mechanism forimparting counter-torque in consideration of valve spring torque,inertia torque, and in-cylinder compression torque, which arise while anintake valve or exhaust valve is being opened or closed. This decreasesthe torque applied to the electric motor, thereby reducing the rating ofthe electric motor.

Patent Document 1: Japanese Patent Laid-open 2005-171786

Patent Document 1: Japanese Patent Laid-open 2005-171937

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

However, the control device disclosed in Patent Document 1 entails acost increase because it newly includes the torque reduction mechanism.In addition, the use of the torque reduction mechanism may result inincreased friction torque between a cam and a valve.

The present invention has been made to solve the above problem. Anobject of the present invention is to provide a variable valve mechanismcontrol device that is capable of reducing the power consumption andrating of an electric motor by using camshaft rotary inertia torque toreduce spring reaction force during a valve lift.

Means for Solving the Problem

The first aspect of the present invention is a variable valve mechanismcontrol device for an internal combustion engine, comprising:

a camshaft on which a cam is mounted to drive a valve that is biased bya valve spring;

an electric motor which rotationally drives the camshaft; and

control means for exercising drive control over the electric motor;

wherein the control means controls the rotary inertia force of thecamshaft so as to be equal to or more than a predetermined value at thebeginning of a valve lift so that the rotary inertia force cancels thespring reaction force of the valve spring.

The second aspect of the present invention is the variable valvemechanism control device according to the first aspect of the presentinvention, wherein the control means controls the rotational position ofthe electric motor so that the rotation speed of the camshaft isdecreased by the spring reaction force exerted during the time intervalbetween the instant at which a valve lift starts and the instant atwhich the maximum lift position is reached, and that the rotation speedof the camshaft is increased by the spring reaction force exerted duringthe time interval between the instant at which the maximum lift positionis reached and the instant at which the valve lift terminates.

The third aspect of the present invention is the variable valvemechanism control device according to the first aspect of the presentinvention, wherein the control means employs the spring reaction forceexerted during the time interval between the instant at which the valvelift starts and the instant at which the maximum lift position isreached as deceleration torque for the rotary inertia force, whileemploying the spring reaction force exerted during the time intervalbetween the instant at which the maximum lift position is reached andthe instant at which the valve lift terminates as acceleration torquefor the rotary inertia force.

The fourth aspect of the present invention is the variable valvemechanism control device according to the first aspect of the presentinvention, wherein, when the rotary inertia force exerted at the end ofthe valve lift is smaller than the predetermined value, the controlmeans requires during a cam base circle slide to the electric motor togenerate such torque that causes said rotary inertia force to be equalto or more than the predetermined value.

The fifth aspect of the present invention is the variable valvemechanism control device according to the first aspect of the presentinvention, wherein the control means inhibits the electric motor togenerate torque opposing the spring reaction force and requires theelectric motor to generate only torque opposing the friction of the camand valve during a valve lift.

The sixth aspect of the present invention is the variable valvemechanism control device according to any one of the first to fifthaspects of the present invention, further comprising:

engine speed change means which raises an engine speed to a value equalto or more than a predetermined value when a requested engine outputvalue is equal to or more than a predetermined value and the enginespeed is in a low rotation speed region where the engine speed is equalto or lower than the predetermined value.

The seventh aspect of the present invention is the variable valvemechanism control device according to any one of the first to fifthaspects of the present invention, further comprising:

an inertia force increase member which is installed in a cam drivesystem having the camshaft and the electric motor to increase thecamshaft rotary inertia force;

wherein the inertia force increase member adjusts the enlargement rangefor an actual operating angle in a low rotation speed region where anengine speed is equal to or lower than a predetermined value.

The eighth aspect of the present invention is the variable valvemechanism control device according to any one of the first to fifthaspects of the present invention, further comprising:

an inertia force change mechanism which can change the camshaft rotaryinertia force when the operating angle of the valve is to be changedwithin a low rotation speed region where an engine speed is equal to orlower than a predetermined value.

The ninth aspect of the present invention is the variable valvemechanism control device according to the first aspect of the presentinvention, wherein, when the cam is to be driven from a stopped state,the control means requires the electric motor to generate such torquethat causes the rotary inertia force to be equal to or more than apredetermined value during a cam base circle slide before the start of avalve lift.

The tenth aspect of the present invention is the variable valvemechanism control device according to the first aspect of the presentinvention, wherein, when the cam is to be driven from a stopped state,the control means requires the electric motor to generate such torquethat causes the rotary inertia force to reach a predetermined initialvalue during a cam base circle slide before the start of a valve lift,and then requires the electric motor to generate such torque that causesthe rotary inertia force at the end of the valve lift to reach apredetermined value greater than the predetermined initial value.

The eleventh aspect of the present invention is the variable valvemechanism control device according to claim 1, wherein, when the cam isto be driven in a normal rotation direction, the control means changesthe rotation speed of the camshaft during a cam base circle slide inaccordance with an engine speed so that the rotation of the camshaftsynchronizes with the rotation of a crankshaft.

The twelfth aspect of the present invention is a variable valvemechanism control device for an internal combustion engine, comprising:

a camshaft on which a cam is mounted to drive a valve that is biased bya valve spring;

an electric motor which rotationally drives the camshaft; and

control means for exercising drive control over the electric motor;

wherein the control means controls the rotational position of theelectric motor so that the cam rotation speed during a valve lift isequal to or lower than the cam rotation speed during a cam base circleslide.

The thirteenth aspect of the present invention is the variable valvemechanism control device according to the first aspect of the presentinvention, wherein the control means increase the rotary inertia forceto a value equal to or more than a predetermined value by impartingtorque of the electric motor during a cam base circle slide so as toswingingly drive the cam, and then synchronizes the rotation of thecamshaft with the rotation of a crankshaft.

The fourteenth aspect of the present invention is the variable valvemechanism control device according to the thirteenth aspect of thepresent invention, further comprising:

startup request acquisition means for acquiring a startup request forthe internal combustion engine;

wherein the control means changes the period for swingingly driving thecam to increase the rotary inertia force in compliance with the startuprequest acquired by the startup request acquisition means.

The fifteenth aspect of the present invention is the variable valvemechanism control device according to the fourteenth aspect of thepresent invention, wherein the control means includes judgment means fordetermining the degree of requested acceleration indicated by thestartup request, applies the torque of the electric motor only during acam base circle slide if the degree of requested acceleration is smallerthan a predetermined value, and applies the torque of the electric motornot only during a cam base circle slide but also during a valve lift ifthe degree of requested acceleration is equal to or more than thepredetermined value.

ADVANTAGES OF THE INVENTION

According to the first aspect of the present invention, the springreaction force is cancelled by the camshaft rotary inertia force. Itmeans that, since the spring reaction force generated during a valvelift is reduced by the camshaft rotary inertia force, the torque thatshould be generated by the electric motor during a valve lift can bereduced. This makes it possible to reduce the power consumption andrating of the electric motor.

According to the second aspect of the present invention, the rotationalposition of the electric motor is controlled so that the camshaftrotation speed is decreased by the spring reaction force generatedduring the period between the instant at which a valve lift starts andthe instant at which the maximum lift position is reached, and that thecamshaft rotation speed is increased by the spring reaction forcegenerated during the period between the instant at which the maximumlift position is reached and the instant at which the valve liftterminates. This enables the camshaft rotary inertia force to reduce thespring reaction force during a valve lift.

According to the third aspect of the present invention, the springreaction force generated during the period between the instant at whicha valve lift starts and the instant at which the maximum lift positionis reached is used as deceleration torque for the camshaft rotaryinertia force, and the spring reaction force generated during the periodbetween the instant at which the maximum lift position is reached andthe instant at which the valve lift terminates is used as accelerationtorque for the camshaft rotary inertia force. This enables the camshaftrotary inertia force to reduce the spring reaction force during a valvelift.

According to the fourth aspect of the present invention, in a case wherethe camshaft rotary inertia force is smaller than a predetermined valueat the end of a valve lift, the electric motor is required to generatesuch torque that makes the camshaft rotary inertia force equal to ormore than the predetermined value during a cam base circle slide. Thetorque required to the electric motor to generate can be smaller duringa cam base circle slide than during a valve lift. It is thereforepossible to avoid an increase in the power consumption and rating of theelectric motor.

According to the fifth aspect of the present invention, the electricmotor is required to generate no counter-spring-reaction-force torquebut only counter-friction torque during a valve lift. This makes itpossible to reduce the torque required to the electric motor to generateduring a valve lift. Thus, the rating of the electric motor can bereduced since the rating of the electric motor can be determined merelyby considering the counter-friction torque.

According to the sixth aspect of the present invention, in a case wherethe requested engine output value is equal to or more than apredetermined value in a low rotation speed region, engine speed isincreased to equal to or more than a predetermined value by the enginespeed change means. Here, since the camshaft rotary inertia forcebecomes smaller in the low rotation speed region than in a high rotationspeed region, the enlargement range for the actual operating anglebecomes greater in the low rotation speed region. When the operatingangle is large, it may not be possible to achieve a requested engineoutput value, since the Atkinson cycle is implemented so that adequatetorque cannot be generated. The sixth aspect of the present inventioncan reduce the enlargement range for the actual operating angle byswitching toward the high rotation speed side. This makes it possible togenerate adequate torque and achieve a requested engine output value.

According to the seventh aspect of the present invention, theenlargement range for the actual operating angle in the low rotationspeed region is adjusted by increasing the camshaft rotary inertia forceby the inertia force increase member. This makes it possible to achievetarget values for fuel efficiency and torque.

According to the eighth aspect of the present invention, the inertiaforce change mechanism can change the camshaft rotary inertia force whenthe valve operating angle is changed in the low rotation speed region.In other words, the enlargement range for the actual operating angle canbe changed by changing the camshaft rotary inertia force, so as toimplement a desired valve operating angle.

According to the ninth aspect of the present invention, when a stoppedcam is to be driven, the electric motor is required to generate suchtorque that makes the camshaft rotary inertia force equal to or morethan the predetermined value during a cam base circle slide before thestart of a valve lift. The camshaft rotary inertia force, which has beenincreased before the start of the valve lift, cancels the springreaction force during the valve lift. Further, since the spring reactionforce does not act on the camshaft during the cam base circle slide, thecamshaft rotary inertia force can be increased even if the torquerequired to the electric motor to generate is small. This makes itpossible to reduce the power consumption of the electric motor when thecam is to be driven from its stopped state. Consequently, the rating ofthe electric motor can be reduced.

According to the tenth aspect of the present invention, when a stoppedcam is to be driven, the electric motor is required to generate suchtorque that makes the camshaft rotary inertia force reach to thepredetermined initial value during a cam base circle slide before thestart of a valve lift. Subsequently, the electric motor is required togenerate such torque that makes the camshaft rotary inertia force reachto a predetermined value greater than the predetermined initial value atthe end of the valve lift. As the torque required to the electric motorto generate is divided, the torque required to the electric motor togenerate before the start of a valve lift is reduced. Therefore, thetenth aspect of the present invention can accept a lower electric motorrating than the ninth aspect.

According to the eleventh aspect of the present invention, the rotationof the camshaft can be synchronized with that of the crankshaft bychanging the camshaft rotation speed during a cam base circle slide inaccordance with the engine speed.

According to the twelfth aspect of the present invention, the rotationalposition of the electric motor is controlled so that the cam rotationspeed during a valve lift is equal to or lower than the cam rotationspeed during a cam base circle slide. This makes it possible to minimizethe torque that is required to the electric motor to generate during avalve lift.

According to the thirteenth aspect of the present invention, thecamshaft rotary inertia force is increased to a value equal to or morethan the predetermined value necessary for normal rotation drive byapplying the torque of the electric motor during a cam base circle slideto swingingly drive the cam. Subsequently, the cam is driven in thenormal direction so that the rotation of the camshaft is synchronizedwith that of the crankshaft. The camshaft rotary inertia force does notdrastically increase to a value equal to or more than the predeterminedvalue, but gradually increases through repeated cam swings. This makesit possible to decrease the electric motor torque, thereby reducing therating of the electric motor.

According to the fourteenth aspect of the present invention, the periodfor swingingly driving the cam to increase the rotary inertia force ischanged in accordance with an internal combustion engine startuprequest. Therefore, the cam can switch from swing drive to normalrotation drive with optimum timing according to the internal combustionengine startup request.

According to the fifteenth aspect of the present invention, the torqueof the electric motor is applied only during a cam base circle slide ifthe degree of requested acceleration indicated by the internalcombustion engine startup request is smaller than the predeterminedvalue. This provides a relatively long period for swinging the cam toincrease the camshaft rotary inertia force. If, on the other hand, thedegree of requested acceleration is not smaller than the predeterminedvalue, the torque of the electric motor is applied not only during a cambase circle slide but also during a valve lift. This makes it possibleto increase the camshaft rotary inertia force in a short period of time.Consequently, the cam can switch from swing drive to normal rotationdrive in a short period of time.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view illustrating the configuration of avariable valve mechanism 10 according to a first embodiment of thepresent invention;

FIG. 2 is an axial view of the first camshaft 18 shown in FIG. 1;

FIG. 3 is a drawing for describing the configuration of the engine 1 inwhich the variable valve mechanism 10 shown in FIG. 1 is mounted

FIG. 4 is a drawing for describing the configuration of a hybrid vehiclesystem according to the first embodiment of the present invention;

FIG. 5 is a perspective view illustrating the essential partconfiguration of a drive mechanism in the hybrid vehicle system shown inFIG. 4;

FIGS. 6A and 6B are drawings for describing the spring reaction forcethat acts on a camshaft during a valve lift;

FIG. 7 is a drawing for describing the motor torque to be generated whenthe cam rotation speed is constant;

FIGS. 8A to 8C show how the spring reaction force acting on the camshaftaffects the cam speed in the first embodiment of the present invention;

FIG. 9 shows how the camshaft rotary inertia force changes in the firstembodiment of the present invention;

FIGS. 10A to 10E show valve lift characteristics and cam rotation speedchanges at various engine speeds in the first embodiment of the presentinvention;

FIG. 11 is a drawing for describing a first modification of the firstembodiment of the present invention;

FIG. 12 is a drawing for describing a second modification of the firstembodiment of the present invention;

FIGS. 13A to 13C show how the spring reaction force acting on a camshaftacts on the cam speed in a second embodiment of the present invention;

FIG. 14 shows a map that defines a target value for the cam rotationspeed during a cam base circle slide;

FIG. 15 shows how the camshaft rotary inertia force changes in thesecond embodiment of the present invention;

FIG. 16 shows how the cam rotation speed changes in the secondembodiment of the present invention;

FIG. 17 shows the relationship between the engine speed NE and actualoperating angle in a third embodiment of the present invention;

FIG. 18 is a collinear drawing for describing a distribution changeoperation that the power distribution mechanism 51 performs when theengine speed NE is to be shifted toward a high rotation speed side;

FIG. 19 shows an inertia force increase section provided in a cam drivesystem according to a fourth embodiment of the present invention;

FIG. 20 shows an inertia force increase section provided in a cam drivesystem according to a modification of the fourth embodiment of thepresent invention;

FIG. 21 shows an inertia force change mechanism according to a fifthembodiment of the present invention;

FIG. 22 shows cam rotation speed changes and motor torque in the sixthembodiment of the present invention;

FIG. 23 shows cam rotation speed changes and motor torque in the seventhembodiment of the present invention;

FIGS. 24A and 24B show cam phase changes and valve lifts in the eighthembodiment of the present invention;

FIGS. 25A to 25C show an example of motor torque that is imparted in theninth embodiment when an engine startup request is generated inaccordance with a catalyst warm-up request;

FIGS. 26A to 26C show an example of motor torque that is imparted in theninth embodiment when an engine startup request is generated inaccordance with an acceleration request; and

FIG. 27 is a flowchart illustrating a routine that the ECU 30 executesin the ninth embodiment. will now be described with reference to.

DESCRIPTION OF REFERENCE NUMERALS

-   -   1 Engine    -   3 Crankshaft    -   10 Variable Valve Mechanism    -   14; 15; 16; 17 Cam    -   18; 19 Camshaft    -   20; 21; 23; 24; 25 Gear    -   22; 26 Motor    -   27 Weight    -   30 ECU    -   44 Transmission    -   51 Power transfer mechanism    -   52 Generator    -   54 Motor    -   60 Battery

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will now be described withreference to the accompanying drawings. Like elements in the drawingsare designated by the same reference numerals and will not beredundantly described.

First Embodiment Configuration of Variable Valve Mechanism

FIG. 1 is a perspective view illustrating the configuration of avariable valve mechanism 10 according to a first embodiment of thepresent invention. As shown in FIG. 1, the variable valve mechanism 10is provided to an engine 1 at the side of an intake valve 11. Thevariable valve mechanism 10 is capable of changing the operating angleand lift amount of the intake valve 11.

The engine 1 is, for example, an in-line four-cylinder gasoline engine.In FIG. 1, the reference numerals #1 to #4 respectively represent thefirst to fourth cylinders of the engine 1. In the engine 1, explosionoccurs in the order of the first, third, fourth, and second cylinders,as is the case with a common engine.

Two intake valves 11 provided for each cylinder 2 are biased towardvalve lifters 13 by the spring reaction force of valve springs 12. Cams14, 15, 16, 17, each of which is related to each cylinder 2, arepositioned above the valve lifters 13.

The cam 14 related to the first cylinder #1 and the cam 17 related tothe fourth cylinder #4 are fastened to a first camshaft 18. The cam 15related to the second cylinder #2 and the cam 16 related to the thirdcylinder #3 are fastened to a second camshaft 19. These camshafts 18, 19are coaxially positioned and capable of rotating each other.

The first camshaft 18 is coaxially fastened to a first driven gear 20.The first driven gear 20 is engaged with a first output gear 21. Thefirst output gear 21 is fastened to the same axis as for the outputshaft of a first motor 22. The configuration described above makes itpossible to transmit the torque of the first motor 22 to the firstcamshaft 18 through the gears 20, 21. In other words, the first motor 22directly drives the cams 14, 17 without regard to a later-describedcrankshaft 3, thereby controlling the intake valve openingcharacteristics of the first cylinder #1 and fourth cylinder #4.

The second camshaft 19 is coaxially fastened to a second driven gear 23.A second output gear 25 meshes with the second driven gear 23 isengaged, via an intermediate gear 24, with a second output gear 25. Thesecond output gear 25 is fastened to the same axis as for the outputshaft of a second motor 26. The configuration described above makes itpossible to transmit the torque of the second motor 26 to the secondcamshaft 19 through the gears 23, 24, 25. In other words, the secondmotor 26 directly drives the cams 15, 16 without regard to thecrankshaft 3, thereby controlling the intake valve openingcharacteristics of the second cylinder #2 and third cylinder #3.

The operation of the variable valve mechanism 10 described above iscontrolled by an ECU (Electronic Control Unit) 30, which serves as acontrol device. More specifically, the ECU 30 issues drive instructionsto the first motor 22 and second motor 26 in accordance with outputsfrom various sensors to control the rotational positions of the motors22, 26.

FIG. 2 is an axial view of the first camshaft 18 shown in FIG. 1. Asshown in FIG. 2, the two cams 14, 17 mounted on the first camshaft 18are arranged so that their cam noses 14 a, 17 a are positioned 180°apart from each other in the circumferential direction of the firstcamshaft 18. The two cams 14, 17 are shaped the same and symmetricalwith respect to a straight line passing through the cam center and camnose.

There are two drive modes for the cams 14, 17: normal rotation drivemode and swing drive mode. In the normal rotation drive mode, the firstmotor 22 continuously rotates in one direction to continuously rotatethe cams 14, 17 in a normal rotation direction. In the swing drive mode,on the other hand, the first motor 22 changes its rotation directionduring a lift of the intake valve 11 to reciprocate the cams 14, 17.

Although the two cams 15, 16 mounted on the second camshaft 19 are notshown in the figure and will not be described in detail, these two cams15, 16 are also arranged so that their cam noses 15 a, 16 a arepositioned 180° apart from each other in the circumferential directionof the second camshaft 19. Further, the second motor 26 can exercisedrive control over these cams 14, 17 to place them in either the normalrotation drive mode or swing drive mode.

[Configuration of Engine]

FIG. 3 illustrates the configuration of the engine 1 in which thevariable valve mechanism 10 shown in FIG. 1 is mounted. The engine 1 hasa cylinder block 6, which includes a piston 5. The piston 5 is connectedto the crankshaft 3 through a crank mechanism. A crank angle sensor 4,which detects the rotation angle of the crankshaft 3, is installed nearthe crankshaft 3.

A cylinder head 7 is attached to the top of the cylinder block 6. Thecylinder head 7 includes an ignition plug 9, which ignites an air-fuelmixture in a combustion chamber 8. The cylinder head 7 has an intakeport 31 that communicates with the combustion chamber 8. Theaforementioned intake valve 11 is positioned in the joint between theintake port 31 and combustion chamber 8. The intake valve 11 isconnected to the above-mentioned variable valve mechanism 10. Aninjector 32 is installed near the intake port 31 to inject fuel into theneighborhood of the intake port 31.

The intake port 31 is connected to an intake path 32. A throttle valve33 is installed in the middle of the intake path 32. The throttle valve33 is an electronically controlled valve that is driven by a throttlemotor 34. The throttle valve 33 is driven in accordance with anaccelerator angle AA, which is detected by an accelerator angle sensor36. A throttle angle sensor 35 is installed near the throttle valve 33to detect a throttle angle TA. An air flow meter 37 is installedupstream of the throttle valve 33. The air flow meter 37 is configuredto detect an intake air amount Ga.

The cylinder head 7 also includes an exhaust port 38, which communicateswith the combustion chamber 8. An exhaust valve 39 is mounted in thejoint between the exhaust port 38 and combustion chamber 8. The exhaustvalve 39 is connected to a variable valve mechanism 40 that has the sameconfiguration as the aforementioned variable valve mechanism 10. Theexhaust port 38 is connected to an exhaust path 41. A catalyst 42 isinstalled in the exhaust path 41 to purify exhaust gas. An air-fuelratio sensor 43 is installed upstream of the catalyst 42 to detect anexhaust air-fuel ratio. The catalyst 42 includes a catalyst bedtemperature sensor 45, which detects a catalyst bed temperature.

The ECU 30 has its output end connected, for instance, to the ignitionplug 9, injector 32, throttle motor 34, and transmission 44 in additionto the aforementioned motors 22, 26. The transmission 44 may be eitheran automatic transmission or a continuously variable transmission. TheECU 30 has its input end connected, for instance, to the crank anglesensor 4, throttle angle sensor 35, accelerator angle sensor 36, airflow meter 37, air-fuel ratio sensor 43, and catalyst bed temperaturesensor 45. The ECU 30 calculates an engine speed (also hereinafterreferred to as the “engine revolution speed”) NE in accordance with anoutput from the crank angle sensor 4.

[Configuration of Hybrid Vehicle System]

The power supply infrastructure of a hybrid vehicle system can be usedto drive the above-mentioned motors 22, 26. FIG. 4 illustrates theconfiguration of a hybrid vehicle system according to the firstembodiment of the present invention. The hybrid vehicle system shown inFIG. 4 includes the aforementioned engine 1, which is one drivingsource, and two other driving sources, namely, a motor generator(hereinafter referred to as the “generator”) 52 and a motor generator(hereinafter referred to as the “motor”) 54.

As shown in FIG. 4, the hybrid vehicle system includes a triaxial powerdistribution mechanism 51. The power distribution mechanism 51 is alater-described planetary gear mechanism. The power distributionmechanism 51 is connected to the generator 52 and motor 54 in additionto the crankshaft 3 of the aforementioned engine 1. The powerdistribution mechanism 51 is also connected to a speed reducer 53. Thespeed reducer 53 is connected to a rotation shaft 57 of a driving wheel55. The driving wheel 55 is provided with a wheel speed sensor 56. Thewheel speed sensor 56 is configured to detect the number of revolutionsor the rotation speed of the driving wheel 55.

The generator 52 and motor 54 are connected to a common inverter 58. Theinverter 58 is connected to a boost converter 59. The boost converter 59is connected to a battery 60. The boost converter 59 converts thevoltage (e.g., 201.6 VDC) of the battery 60 to a high voltage (e.g., 500VDC). The inverter 58 converts the high DC voltage, which is generatedby the boost converter 59, to an AC voltage (e.g., 500 VAC). Thegenerator 52 and motor 54 exchange electrical power with the battery 60through the inverter 58 and boost converter 59.

As shown in FIG. 4, the ECU 30 is connected not only to theaforementioned engine 1 but also, for instance, to the powerdistribution mechanism 51, generator 52, speed reducer 53, motor 54,wheel speed sensor 56, inverter 58, boost converter 59, and battery 60.The ECU 30 controls the drive amount or power generation amount of thegenerator 52 and motor 54. The ECU 30 also acquires information aboutthe state of charge (SOC) of the battery 60.

[Essential Part Configuration of Drive Mechanism]

FIG. 5 is a perspective view illustrating the essential partconfiguration of a drive mechanism in the hybrid vehicle system shown inFIG. 4.

As shown in FIG. 5, the power distribution mechanism 51 includes a sungear 61, a ring gear 62, a plurality of pinion gears 63, and a carrier64. The sun gear 61, which is an external gear, is fastened to a hollowsun gear shaft 65. The crankshaft 3 of the engine 1 runs through thehollow of the sun gear shaft 65. The ring gear 62, which is an internalgear, is concentric with the sun gear 61. The plurality of pinion gears63 are positioned so as to engage with both the sun gear 61 and ringgear 62. The pinion gears 63 are rotatably retained by the carrier 64.The carrier 64 is coupled to the crankshaft 3. In other words, the powerdistribution mechanism 51 is a planetary gear mechanism that performs adifferential operation by using the sun gear 61, ring gear 62, andpinion gears 63 as rotational elements.

The speed reducer 53 includes a motive power outputting gear 66, whichis used for transmitting motive power. The motive power outputting gear66 is coupled to the ring gear 62 of the power distribution mechanism51. The motive power outputting gear 66 is also coupled to a powertransmission gear 68 through a chain 67. The power transmission gear 68is coupled to a gear 70 through a rotation shaft 69. The gear 70 iscoupled to a differential gear (not shown) that rotates the rotationshaft 57 of the driving wheel 55.

The generator 52 includes a rotor 71 and a stator 72. The rotor 71 ismounted on the sun gear shaft 65, which rotates together with the sungear 61. The generator 52 is configured so that it can be driven notonly as an electric motor for rotating the rotor 71 but also as a powergenerator for generating electromotive force by using the rotation ofthe rotor 71. Further, the generator 52 functions as a starter at enginestartup.

The motor 54 includes a rotor 73 and a stator 74. The rotor 73 ismounted on a ring gear shaft 75, which rotates together with the ringgear 62. The motor 54 is configured so that it not only can function asan electric motor for rotating the rotor 73 but can also be driven as apower generator for generating electromotive force by using the rotationof the rotor 73.

The power distribution mechanism 51 can distribute the motive power ofthe engine 1, which is input from the carrier 64, to the sun gear 61,which is connected to the generator 52, and to the ring gear 62, whichis connected to the rotation shaft 57, in accordance with their gearratio. The power distribution mechanism 51 can also combine the motivepower of the engine 1, which is input from the carrier 64, and themotive power of the generator 52, which is input from the sun gear 61,and output the combined motive power to the ring gear 62. Further, thepower distribution mechanism 51 can combine the motive power of thegenerator 52, which is input from the sun gear 61, and the motive powerinput from the ring gear 62, and output the combined motive power to thecarrier 64.

The ECU 30 calculates the torque required for the overall vehicle inaccordance with the rotation speed of the driving wheel 55, which isdetected by the wheel speed sensor 56, and the accelerator angle AA,which is detected by the accelerator angle sensor 36. To obtain thetorque required for the overall vehicle, the ECU 30 distributes drivingforce to the engine 1, generator 52, and motor 54 while considering thestate of charge (SOC) of the battery 60. In other words, the ECU 30calculates the torque required for the engine 1 (hereinafter referred toas the “required engine torque”) and the torque required for thegenerator 52 and motor 54.

The ECU 30 can provide improved fuel efficiency by stopping the engine 1during deceleration, braking, or low-speed rotation (e.g., at a rotationspeed of lower than 1000 rpm).

Features of First Embodiment

The variable valve mechanism 10 described above uses the motors 22, 26to rotate the camshafts 18, 19. The motor rating is determined so as tosupport the load imposed on the motors. The load imposed on the motorsincludes, for instance, valve spring reaction force, camshaft rotaryinertia force, and friction torque. The spring reaction force, inparticular, greatly affects the motor size and rating.

FIGS. 6A and 6B illustrate the spring reaction force that acts on acamshaft during a valve lift. More specifically, FIG. 6A shows thespring reaction force that acts during a valve lift ascent, whereas FIG.6B shows the spring reaction force that acts during a valve liftdescent. For the sake of brevity, the cam 17 mounted on the camshaft 18is not shown in the figures or described below.

During a valve lift ascent (for valve opening), the cam 14 pushes down avalve spring 12 as shown in FIG. 6A. Therefore, the spring reactionforce oriented in a direction opposite the rotation direction of the cam14 (hereinafter referred to as the “cam rotation direction”) acts on thecamshaft 18.

During a valve lift descent (for valve closing), on the other hand, thespring reaction force of the valve spring 12 pushes the cam 14 as shownin FIG. 6B. Therefore, the spring reaction force oriented in the samedirection as the cam rotation direction acts on the camshaft 18.

Meanwhile, the motors 22, 26 provide phase control over the cam. Itmeans that the rotation of the cam is synchronized with that of thecrankshaft. Conventionally, control is exercised to provide a constantcam rotation speed (half the engine speed NE).

FIG. 7 illustrates the motor torque to be generated when the camrotation speed is constant. When control is exercised to provide aconstant cam rotation speed, it is necessary, as shown in FIG. 7, that amotor generate torque opposing the aforementioned spring reaction force(hereinafter referred to as the “counter-spring-reaction-force torque”).In this instance, the motor torque is the sum of thecounter-spring-reaction-force torque and friction torque. When thecounter-spring-reaction-force torque is to be generated with a motor,the power consumption of the motor increases. Thus, a high motor ratingis required.

According to Patent Document 1 described above, the use of a torquereduction mechanism reduces the spring torque (spring reaction force).However, the addition of the torque reduction mechanism entails a costincrease. It should also be noted that the use of the torque reductionmechanism results in increased friction torque.

Under the above circumstances, the first embodiment increases the rotaryinertia force of the camshaft 18 (hereinafter referred to as the“camshaft rotary inertia force”) before the start of a valve lift, asdescribed in detail below. The camshaft rotary inertia force is employedto cancel the spring reaction force of the valve spring 12.

FIGS. 8A to 8C illustrate how the spring reaction force acting on thecamshaft affects the cam speed in the first embodiment. FIG. 9 shows howthe camshaft rotary inertia force changes in the first embodiment.

First of all, as shown in FIG. 9, the camshaft rotary inertia force isincreased to a value equal to or more than a predetermined value (e.g.,2 Nm) before the start of a lift. The predetermined value represents thecamshaft rotary inertia force that can achieve a valve lift withoutcausing the motor to generate the counter-spring-reaction-force torqueduring a valve lift.

During a valve lift ascent (during the time interval between the instantat which the lift starts and the instant at which the maximum lift isprovided), the spring reaction force oriented in a direction oppositethe direction of cam rotation acts on the camshaft 18 as shown in FIG.8A. In this instance, the motor is not required to generate thecounter-spring-reaction-force torque. In other words, the motor does notgenerate the counter-spring-reaction-force torque. Then, the springreaction force reduces the cam rotation speed. In other words, thespring reaction force works as deceleration torque for the camshaftrotary inertia force. Consequently, the camshaft rotary inertia forcegradually decreases from the aforementioned predetermined value as shownin FIG. 9.

During a subsequent valve lift descent (during the time interval betweenthe instant at which the maximum lift is provided and the instant atwhich the lift is terminated), the spring reaction force oriented in thesame direction as the direction of cam rotation acts on the camshaft 18as shown in FIG. 8B. In this instance, the motor is not required togenerate the counter-spring-reaction-force torque either as is the casewith the valve lift ascent described above. The spring reaction forcethen increases the cam rotation speed. In other words, the springreaction force works as acceleration torque for the camshaft rotaryinertia force. Consequently, the camshaft rotary inertia force graduallyincreases and reaches the aforementioned predetermined value at the endof the lift, as shown in FIG. 9.

During a subsequent cam base circle slide, the cam rotation speed iscontrolled and rendered equal to the engine speed NE×½+correction term αin order to synchronize the cam rotation phase with the rotation of thecrankshaft 3 as shown in FIG. 8C. Further, since the cam 14 does notcome into contact with a valve lifter 13 during a cam base circle slide,the spring reaction force does not act on the camshaft 18. In thisinstance, therefore, the motor is not required to generate thecounter-spring-reaction-force torque either. Consequently, the camshaftrotary inertia force is kept constant as shown in FIG. 9.

As described above, the camshaft rotary inertia force cancels the springreaction force in the first embodiment. During the interval between thestart of a lift and the end of the lift, therefore, it is necessary thatonly the counter-friction torque be generated by the motor as shown inFIG. 9. This makes it possible to reduce the power consumption andrating of the motor.

FIGS. 10A to 10E show valve lift characteristics and cam rotation speedchanges at various engine speeds in the first embodiment. Morespecifically, FIG. 10A shows valve lift characteristics and cam rotationspeed changes at an engine speed NE of 1000 rpm; FIG. 10B shows the sameat an engine speed NE of 2000 rpm; FIG. 10C shows the same at an enginespeed NE of 3000 rpm; FIG. 10D shows the same at an engine speed NE of4000 rpm; and FIG. 10E shows the same at an engine speed NE of 5000 rpm.In FIGS. 10A to 10E, a curve marked “Conventional” represents a casewhere control is exercised so that the cam rotation speed is half theengine speed NE at all times.

When the engine speed NE is 1000 rpm (that is, when the engine speed islow), the cam rotation speed and camshaft rotation speed are lower thanwhen the engine speed is high, as indicated in the upper half of FIG.10A. The camshaft rotary inertia force is, therefore, smaller at a lowengine speed than at a high engine speed. Thus, the spring reactionforce changes the cam rotation speed by a greater amount at a low enginespeed. As a result, the operating angle becomes larger and the liftcurve becomes deformed as compared to those in a conventional case.

The first embodiment controls the motor position so as to obtain theindicated lift curves. More concretely, lift curve maps indicated in theupper halves of FIGS. 10A to 10E are prepared for various engine speedsNE. Further, the motor position is controlled so that the valve liftamount changes in accordance with a lift curve map for a particularengine speed NE. The indicated lift curves are lift curves that areobtained when the motor torque is minimized, that is, when the springreaction force is completely cancelled by the camshaft rotary inertiaforce.

When the motor is driven so as to obtain the lift curves shown in theupper half of FIG. 10A, the cam rotation speed changes as indicated inthe lower half of FIG. 10A. The cam rotation speed attained during a cambase circle slide before the start of a valve lift is approximately 900rpm. Therefore, the correction term α shown in FIG. 8C is 900 rpm−500rpm=400 rpm. The cam rotation speed attained when the maximum lift isprovided is 100 rpm.

Further, an increase in the engine speed NE reduces not only thedifference between conventional lift curves and lift curves according tothe present invention but also the correction term α for the camrotation speed.

As described above, the first embodiment can reduce the spring reactionforce between the start and end of a lift by allowing the camshaftrotary inertia force to cancel the spring reaction force. Thus, only thecounter-friction torque becomes the motor toque during a valve lift.Consequently, the power consumption and rating of the motor can bereduced. This makes it possible to drive the motor with only the powersupply for a normal engine system and without having to use the powersupply infrastructure of a hybrid system.

Further, the first embodiment can reduce the power consumption andrating of the motor without using a torque reduction mechanismdisclosed, for instance, in Patent Document 1 described above. Thismakes it possible to achieve cost reduction and avoid an increase in thefriction torque.

(Modifications)

A first modification of the first embodiment will now be described withreference to FIG. 11.

In the first embodiment, the cam rotation speed is constant during a cambase circle slide (see FIGS. 10A to 10E); therefore, the camshaft rotaryinertia force is also constant. However, the camshaft rotary inertiaforce may be increased during a cam base circle slide.

FIG. 11 is a drawing for describing the first modification of the firstembodiment. More specifically, FIG. 11 shows a case where the camshaftrotary inertia force is increased during a cam base circle slide. Asshown in FIG. 11, the camshaft rotary inertia force is equal to thepredetermined value at the start of a lift, but smaller than thepredetermined value at the end of a lift.

To further reduce the power consumption and rating of the motor, thefirst modification generates a motor torque so that the camshaft rotaryinertia force reaches the predetermined value during a cam base circleslide after the end of a lift. Since the spring reaction force does notact on the camshaft during a cam base circle slide, a small motor torquecan increase the camshaft rotary inertia force to the predeterminedvalue. This makes it possible to reduce the motor rating.

Further, the motor may be required to generate torque during a lift sothat the camshaft rotary inertia force reaches the predetermined valueat the end of a lift. This causes the motor to generate thecounter-spring-reaction-force torque during a lift as in a conventionalmanner. In marked contrast to the conventional case, however, part ofthe spring reaction force is cancelled by the camshaft rotary inertiaforce. Therefore, the counter-spring-reaction-force torque required tothe motor to generate is smaller than in the conventional case. As aresult, the power consumption and rating of the motor can be made lowerthan in the conventional case.

FIG. 12 illustrates a second modification of the first embodiment.

In the first embodiment, the spring reaction force and camshaft rotaryinertia force are completely cancelled.

In the second modification, the value (the predetermined value)representing the camshaft rotary inertia force exerted before the startof a valve lift is set to be smaller than indicated in FIG. 9.Therefore, the camshaft rotary inertia force does not cancel the entirespring reaction force; however, part of the camshaft rotary inertiaforce is cancelled. The counter-spring-reaction-force torque, which isagainst the spring reaction force that is not cancelled, is required tothe motor to generate. Therefore, the motor torque according to thesecond modification is the sum of the counter-spring-reaction-forcetorque and friction torque as shown in FIG. 12. The second modificationprovides a motor torque that is smaller than a conventional motortorque, as shown in FIG. 12. Consequently, the power consumption andrating of the motor can be made lower than in the conventional case.

In the first embodiment and its modifications, the engine 1 correspondsto the “internal combustion engine” according to the first aspect of thepresent invention; the variable valve mechanism 10 corresponds to the“variable valve mechanism” according to the first aspect of the presentinvention; and the ECU 30 corresponds to the “control means” accordingto the first to fifth aspects and the ninth to twelfth aspects of thepresent invention. Further, in the first embodiment and itsmodifications, the valve spring 12 corresponds to the “valve spring”according to the first aspect of the present invention; the valve 11corresponds to the “valve” according to the first aspect of the presentinvention; the cams 14-17 correspond to the “cam” according to the firstaspect of the present invention; the camshafts 18, 19 correspond to the“camshaft” according to the first aspect of the present invention; andthe electric motors 22, 26 correspond to the “electric motor” accordingto the first aspect of the present invention.

Second Embodiment

A second embodiment of the present invention will now be described withreference to FIGS. 13 to 16.

The hardware shown in FIGS. 1 to 5 can be used as a system according tothe second embodiment.

Features of Second Embodiment

The first embodiment has been described in conjunction with a case wherethe cams 14-17 are driven in the normal rotation drive mode. On theother hand, the second embodiment will be described in conjunction witha case where the cams 14-17 are driven in the swing drive mode. Asdescribed with reference to FIG. 2, the above system can be used toexecute the swing drive mode.

FIGS. 13A to 13C illustrate how the spring reaction force acting on acamshaft acts on the cam speed in the second embodiment. FIG. 14 shows amap that defines a target value for the cam rotation speed during a cambase circle slide. FIG. 15 shows how the camshaft rotary inertia forcechanges in the second embodiment. FIG. 16 shows how the cam rotationspeed changes in the second embodiment.

During a cam base circle slide shown in FIG. 13A, that is, before thecam 14 comes into contact with the valve lifter 13, the cam rotationspeed is raised to a target value. The map shown, for instance, in FIG.14 is referenced to determine the target value in accordance with theoperating angle and engine speed NE. The camshaft rotary inertia forceis then increased, as shown in FIG. 15, to a value equal to or more thanthe predetermined value before the start of a lift as is the case withthe first embodiment.

During a subsequent valve lift ascent (from a lift starts to the maximumlift), the spring reaction force oriented in a direction opposite thedirection of cam rotation acts on the camshaft 18 as shown in FIG. 13B.In this instance, the motor is controlled so as not to generate thecounter-spring-reaction-force torque. The spring reaction force thenreduces the cam rotation speed as shown in FIG. 16. In other words, thespring reaction force works as deceleration torque for the camshaftrotary inertia force. Consequently, the camshaft rotary inertia forcegradually decreases from the aforementioned predetermined value as shownin FIG. 15.

During a subsequent valve lift descent (from the maximum lift to atermination of the lift), the spring reaction force oriented in the samedirection as the direction of cam rotation acts on the camshaft 18 asshown in FIG. 13C. In the second embodiment, the cam 14 is driven in theswing drive mode; therefore, the cam rotates in a direction opposite thecam rotation direction shown in FIG. 13B. In this instance, the motor iscontrolled so as not to generate the counter-spring-reaction-forcetorque either as is the case with the valve lift ascent described above.The spring reaction force then increases the cam rotation speed as shownin FIG. 16. FIG. 16 shows the cam rotation speed relative to the camrotation direction. Since the spring reaction force works asacceleration torque for the camshaft rotary inertia force, the camshaftrotary inertia force gradually increases.

In the second embodiment, the camshaft rotary inertia force cancels thespring reaction force as described above. Therefore, only thecounter-friction torque needs to be generated by the motor, as shown inFIG. 15, during the interval between the start and end of a lift. Thismakes it possible to reduce the power consumption and rating of themotor.

As described above, the second embodiment can reduce the spring reactionforce during the interval between the start and end of a lift byallowing the camshaft rotary inertia force to cancel the spring reactionforce even in the swing drive mode. Therefore, the second embodimentprovides the same advantages as the first embodiment, which has beendescribed earlier.

Third Embodiment

A third embodiment of the present invention will now be described withreference to FIGS. 17 and 18.

The hardware shown in FIGS. 1 to 5 can be used as a system according tothe third embodiment.

Features of Third Embodiment

In a low rotation speed region where, for example, the engine speed NEis equal to or lower than 2000 rpm, the camshaft rotary inertia force issmaller than in a high rotation speed region. Therefore, in a case wherethe camshaft rotary inertia force is employed to cancel the springreaction force as in the present invention, change amount in thecamshaft rotary inertia force due to the spring reaction force becomeslarge. In such an instance, the actual operating angle is larger in thelow rotation speed region than in the high rotation speed region asindicated in FIGS. 10A to 10E and FIG. 17. FIG. 17 shows therelationship between the engine speed NE and actual operating angle. Inan example shown in FIG. 17, the employed cam has a base circle thatprovides an operating angle of 210° when the cam is rotationally drivenat a constant speed. In the example shown in FIG. 17, the actualoperating angle is increased to 280° when the engine speed NE is 1000rpm.

A solid line in FIG. 17 shows how the actual operating angle changeswhen the variable valve mechanism 10 is mounted in the hybrid vehicleengine 1 shown in FIG. 4. A one-dot chain line in FIG. 17, on the otherhand, shows how the actual operating angle changes when the variablevalve mechanism 10 is mounted in a normal engine that has no drivingsource other than an engine. When the variable valve mechanism 10 ismounted in a normal engine, provision is made so as not to exceed amaximum actual operating angle of 270° that allows an air-fuel mixtureto be ignited during idling (200 rpm).

Meanwhile, when the actual operating angle increases, the Atkinson cycleis implemented so that the fuel efficiency improves, although the torquedecreases. If, in this instance, a great driving force is requested insuch a low rotation speed region, the driving force may not be generatedin compliance with such a driving force request.

As such being the case, the third embodiment shifts the engine speed NEtoward a high rotation speed side if the requested driving force isequal to or more than a predetermined value while the engine speed is ina low rotation speed region. FIG. 18 is a collinear drawing fordescribing a distribution change operation that the power distributionmechanism 51 performs when the engine speed NE is to be shifted toward ahigh rotation speed side. As indicated in FIG. 18, increasing the amountof power supply to the generator 52 increases the rotation speed of thesun gear 61. This makes it possible to shift the engine speed NE towarda high rotation speed side.

The actual operating angle can be made smaller than in a low rotationspeed region by shifting the engine speed NE toward a high rotationspeed side. Therefore, an actual compression ratio can be increased toincrease the torque. Consequently, the driving force can be generated incompliance with a driving force request even when a great driving forceis requested.

(Modification)

In the third embodiment, the power distribution mechanism 51 shifts theengine speed NE toward a high rotation speed side. Alternatively,however, the engine speed NE may be shifted toward a high rotation speedside by controlling the speed reduction ratio of the speed reducer 44.Even when the ECU 30 exercises speed reduction ratio control, the actualcompression ratio can be increased; therefore, it is possible to providethe same advantages as the third embodiment.

In the third embodiment and its modification, the power distributionmechanism 51 and transmission 44 correspond to the “engine speed changemeans” according to the sixth aspect of the present invention.

Fourth Embodiment

A fourth embodiment of the present invention will now be described withreference to FIG. 19.

FIG. 19 shows an inertia force increase section provided in a cam drivesystem according to the fourth embodiment. As shown in FIG. 18, the camdrive system includes the camshaft 18, gears 23, 24, 25, and motor 26.In the fourth embodiment, a weight 27 is attached to an end of thecamshaft 18 as shown in FIG. 18.

Features of Fourth Embodiment

As described in conjunction with the third embodiment, when the camshaftrotary inertia force is employed to cancel the spring reaction force asin the present invention, the amount of camshaft rotary inertia forcechange increases in a low rotation speed region. As a result, theenlargement range for the actual operating angle is greater in the lowrotation speed region than in the high rotation speed region.

As regards an engine that places emphasis on fuel efficiency in the lowrotation speed region, the Atkinson cycle is implemented; therefore, noparticular problem arises no matter whether the enlargement range forthe actual operating angle is great. For an engine that places emphasison torque in the low rotation speed region, on the other hand, it ispreferred that the enlargement range for the actual operating angle beminimized to obtain the actual compression ratio.

Meanwhile, if the camshaft rotary inertia force can be increased, changein the camshaft rotary inertia force during a valve lift caused by thespring reaction force decreases. As a result, the enlargement range forthe actual operating angle can be reduced.

In the fourth embodiment, the weight 27 is attached to an end of thecamshaft 18. The addition of the weight 27 provides a greater camshaftrotary inertia force than when the weight 27 is not added. Therefore,the enlargement range for the actual operating angle in the low rotationspeed region can be made smaller than when the weight 27 is not added.Consequently, the actual compression ratio can be obtained in the lowrotation speed region as well. This makes it possible to obtain anadequate torque.

Further, the heavier the weight 27, the smaller the amount of camshaftrotary inertia force change, and thus the smaller the enlargement rangefor the actual operating angle in the low rotation speed region.Therefore, a desired torque (according to a design value) can beobtained in the low rotation speed region by adjusting the weight of theweight 27.

(Modifications)

In the fourth embodiment, the weight 27 is attached to an end of thecamshaft 18. However, the weight 27 may alternatively be attached to anend of a motor drive shaft 26A as shown in FIG. 20. FIG. 20 shows theinertia force increase section for the cam drive system according to amodification of the fourth embodiment. Another alternative would be toattach the weight 27 to the gears 23, 24, 25. These modificationsprovide the same advantages as the fourth embodiment because they canreduce the amount of camshaft rotary inertia force change during a valvelift.

Further, the spring constant of the valve spring 12 may be greater thanits design value. In such an instance, it may not be possible tominimize the motor torque by exercising motor control so as to obtainthe lift curves shown in the upper halves of FIGS. 10A to 10E. In otherwords, the actual spring reaction force may be greater than the springreaction force calculated in accordance with the design value.Therefore, complete cancel may not be provided by the camshaft rotaryinertia force. Then, it may be necessary to require the motor togenerate the counter-spring-reaction-force torque during a valve lift.Consequently, adding the weight 27 causes the camshaft rotary inertiaforce increase, thereby being capable of minimizing the motor torquewhen the spring constant is greater than its design value.

In the fourth embodiment and its modifications, the camshaft 18, gears23, 24, 25, and motor 26 correspond to the “cam drive system” accordingto the seventh aspect of the present invention; and the weight 27corresponds to the “inertia force increase section” according to theseventh aspect of the present invention.

Fifth Embodiment

A fifth embodiment of the present invention will now be described withreference to FIG. 21.

FIG. 21 shows an inertia force change mechanism according to the fifthembodiment of the present invention. As shown in FIG. 21, the inertiaforce change mechanism 28 is mounted on the outer circumference of thecamshaft 18. The inertia force change mechanism 28 includes an oilpassage 28A, which communicates with an oil passage 18A in the camshaft18. A weight 28B is positioned in the oil passage 28A. The oil passage28A is provided with a spring 28C that biases the weight 28B toward theinside of the camshaft 18 (toward the center).

If the hydraulic pressure applied to the oil passage 28A through the oilpassage 18A is smaller than the biasing force of the spring 28C, theweight 28B is biased toward the inside of the camshaft 18. If, on theother hand, the hydraulic pressure applied to the oil passage 28A isgreater than the biasing force of the spring 28C, the weight 28B movesoutward.

Features of Fifth Embodiment

The power consumption and rating of the motor can be reduced by allowingthe camshaft rotary inertia force to cancel the spring reaction force asdescribed above.

Meanwhile, the variable valve mechanism 10 shown in FIG. 1 can controlthe camshaft rotation speed without regard to the crankshaft 3, therebycan change the operating angle.

However, when the motor rating is reduced, no more extra motor torqueexists so that it may be impossible to change the operating angleparticularly in the low rotation speed region. Further, if an attempt ismade to obtain extra motor torque, the motor rating becomes as high asin the conventional case.

Therefore, when the operating angle is to be decreased within the lowrotation speed region, the fifth embodiment moves the weight 28B outwardby applying engine oil pressure to the oil passage 28A. The camshaftrotary inertia force can then be increased. This makes it possible toreduce the aforementioned enlargement range for the actual operatingangle and switch to a small operating angle.

When, on the other hand, the operating angle is to be increased withinthe low rotation speed region, the fifth embodiment moves the weight 28Binward by applying no engine oil pressure to the oil passage 28A. Thecamshaft rotary inertia force can then be decreased. This makes itpossible to increase the aforementioned enlargement range for the actualoperating angle and switch to a large operating angle.

Consequently, even when the motor rating is low, the fifth embodimentcan change the camshaft rotary inertia force by repositioning the weight28B. As a result, the operating angle can be changed.

In the fifth embodiment, the inertia force change mechanism 28corresponds to the “inertia force change mechanism” according to theeighth aspect of the present invention.

Sixth Embodiment

A sixth embodiment of the present invention will now be described withreference to FIG. 22.

The hardware shown in FIGS. 1 to 5 can be used as a system according tothe sixth embodiment.

Features of Sixth Embodiment

The first and second embodiments have been described in conjunction withmotor drive control that is initiated when the cam and camshaft arerotating.

The sixth embodiment will be described in conjunction with motor drivecontrol that is initiated when the cam and camshaft are stopped. FIG. 22shows cam rotation speed changes and motor torque in the sixthembodiment.

As shown in FIG. 22, the cam is stopped at a base circle before thebeginning of startup. Therefore, the cam rotation speed and camshaftrotation speed are zero. Further, the camshaft rotary inertia force isalso zero.

During a subsequent cam base circle slide, that is, during the timeinterval between the instant at which startup begins and the instant atwhich a lift is about to begin, the cam rotation speed is raised to atarget value. As a result, the camshaft rotary inertia force reaches apredetermined value. In this instance, no spring reaction force acts onthe camshaft. Therefore, acceleration can be achieved by a smaller motortorque than when acceleration is achieved during a valve lift. When anextra motor torque is available, the acceleration is executed slowly sothat the cam rotation speed reaches the target value at the beginning ofa lift. The reason is that slow acceleration requires less motor powerconsumption than sudden acceleration.

During the subsequent time interval between the instant at which a liftstarts and the instant at which the maximum lift is provided, only thecounter-friction torque is required to the motor to generate withoutrequiring the motor to generate the counter-spring-reaction-forcetorque. Therefore, the spring reaction force decreases the cam rotationspeed, thereby gradually decreasing the camshaft rotary inertia force.

During the time interval between the instant at which the maximum liftis provided and the instant at which a valve lift terminates, only thecounter-friction torque is required to the motor to generate alsowithout requiring the motor to generate thecounter-spring-reaction-force torque. Therefore, the spring reactionforce increases the cam rotation speed, thereby gradually increasing thecamshaft rotary inertia force. Since the cam rotation speed reaches theaforementioned target value again at the end of a valve lift, thecamshaft rotary inertia force reaches the predetermined value again.

As described above, the sixth embodiment increases the cam rotationspeed before the start of a lift to increase the camshaft rotary inertiaforce to a value equal to or more than the predetermined value, therebyallowing the camshaft rotary inertia force to cancel the spring reactionforce. Therefore, it is necessary that only the counter-friction torquebe generated by the motor during a valve lift as shown in FIG. 22.Further, during a cam base circle slide before the start of a lift, thecam rotation speed can be increased by a relatively small motor torque.In other words, the motor torque for increasing the cam rotation speedis smaller than the counter-spring-reaction-force torque. Therefore, itis possible to reduce the power consumption and rating of the motor.

In the sixth embodiment, the ECU 30 corresponds to the “control means”according to the ninth aspect of the present invention.

Seventh Embodiment

A seventh embodiment of the present invention will now be described withreference to FIG. 23.

The hardware shown in FIGS. 1 to 5 can be used as a system according tothe seventh embodiment.

Features of Seventh Embodiment

In the sixth embodiment described earlier, the motor torque forincreasing the cam rotation speed before the start of a lift is greaterthan the motor torque used during a valve lift. In such an instance, thepower consumption and rating of the motor are determined by the motortorque used at the beginning of cam drive.

As such being the case, the seventh embodiment will be described inconjunction with a method of reducing the motor torque during the timefor cam drive start (that is, during the time for cam rotation speedacceleration before the start of a lift) FIG. 23 shows cam rotationspeed changes and motor torque in the seventh embodiment.

As shown in FIG. 23, the cam rotation speed is raised to an initialtarget value during a cam base circle slide, that is, during the timeinterval between the instant at which startup begins and the instant atwhich a lift is about to begin. The initial target value is smaller thanthe target value used in the sixth embodiment. Therefore, the motortorque required for raising the cam rotation speed to the second targetvalue is smaller than the motor torque required for raising the camrotation speed to the above-mentioned target value.

During the subsequent time interval between the instant at which a liftstarts and the instant at which the maximum lift is provided, only thecounter-friction torque is required to the motor to generate withoutrequiring the motor to generate the counter-spring-reaction-forcetorque. Therefore, the spring reaction force decreases the cam rotationspeed, thereby gradually decreasing the camshaft rotary inertia force.

Before the start of a lift, the cam rotation speed is merely raised tothe initial target value. If this condition is allowed to continue, thecam rotation speed does not reach the target value at the end of a lift.Therefore, the torque for raising the cam rotation speed is required tothe motor to generate during the time interval between the instant atwhich the maximum lift is provided and the instant at which a valve liftterminates. The motor torque required in this stage is equal to orsmaller than the motor torque required before the start of a lift.Generating such motor torque ensures that the cam rotation speed reachesthe target value at the end of a lift.

As described above, the seventh embodiment increases the cam rotationspeed to the initial target value, which represents a lower cam rotationspeed than the target value, before the start of a lift, and generatesmotor torque during a cam lift so that the cam rotation speed reachesthe target value at the end of a lift. Therefore, the motor torquerequired for the start of cam drive is smaller in the seventh embodimentthan in the sixth embodiment. Consequently, the power consumption andrating of the motor can be reduced.

In the seventh embodiment, the ECU 30 corresponds to the “control means”according to the tenth aspect of the present invention.

Eighth Embodiment

An eighth embodiment of the present invention will now be described withreference to FIGS. 24A and 24B.

The hardware shown in FIGS. 1 to 5 can be used as a system according tothe eighth embodiment.

Features of Eighth Embodiment

At the time of engine startup, no camshaft rotary inertia force exists.If the camshaft rotary inertia force is smaller than a peak torque Tpshown in FIG. 7, a cam lobe cannot be overridden. It means that the camcannot be driven in a normal rotation direction.

In the seventh embodiment, which has been described earlier, the camrotation speed is raised to the initial target value by imparting motortorque to the camshaft during a cam base circle slide, that is, duringthe time interval between the instant at which engine startup begins andthe instant at which a valve lift is about to begin. Subsequently, thecam rotation speed is raised to the final target value by impartingmotor torque during the time interval between the instant at which themaximum lift is provided and the instant at which the valve liftterminates. As described above, the motor torque is imparted in twosteps to reduce the motor rating and increase the camshaft rotaryinertia force to a value not smaller than the peak torque Tp.

The eighth embodiment will be described in conjunction with a method forfurther reducing the motor rating than that in the seventh embodiment,which has been described earlier. FIGS. 24A and 24B show cam phasechanges and valve lifts in the eighth embodiment. More specifically,FIG. 24A shows cam phase changes, whereas FIG. 24B shows the valve liftsof the first cylinder #1 and fourth cylinder #4.

At time t0, which is indicated in FIGS. 24A and 24B, an engine startupsequence begins. This engine startup sequence is also employed as anengine restart sequence. Motor torque is imparted to the camshaft duringthe interval between time t0 and time t1, which is the time for startinga valve lift for the first cylinder #1, that is, during a cam basecircle slide between the beginning of engine startup and the start of avalve lift. The cam rotation speed then increases to increase thecamshaft rotary inertia force. The motor torque imparted between time t0and time t1 can be smaller than the motor torque imparted before thestart of a lift in the seventh embodiment. Therefore, the motor ratingcan be reduced.

During a subsequent valve lift between time t1 and time t2, no motortorque is imparted to the camshaft. Then, during the interval betweentime t2 at which the valve lift for the first cylinder #1 terminates andtime t3 at which a valve lift for the fourth cylinder #4 starts, motortorque oriented in a direction opposite the torquing direction employedbetween time t0 and time t1 is imparted to the camshaft. This ensuresthat the cam rotation speed at time t3 is higher than the cam rotationspeed at time t1. As a result, the camshaft rotary inertia force at timet3 is greater than the camshaft rotary inertia force at time t1. The camphase then increases to increase the cam swing range.

During the subsequent interval between time t4 at which the valve liftfor the fourth cylinder #4 terminates and time t5 at which a valve liftfor the first cylinder #1 starts, motor torque oriented in a directionopposite the torquing direction used between time t2 and time t3 isimparted to the camshaft. This ensures that the cam rotation speed attime t5 is higher than the cam rotation speed at time t3. As a result,the camshaft rotary inertia force at time t5 is greater than thecamshaft rotary inertia force at time t3. As a result, the cam phasefurther increases so as to further increase the cam swing range.

During a subsequent cam base circle slide between time t6 and time t7,between time t8 and time t9, and between time t10 and time t11, motortorque is imparted to the camshaft in the same manner as describedabove. Then, the cam rotation speed increases as the time elapses fromt7 through t9 to t11, thereby gradually increasing the camshaft rotaryinertia force. As a result, the cam phase gradually increases so as togradually increase the cam swing range. This causes the valve liftamount to gradually increase.

When the camshaft rotary inertia force necessary for driving the cam ina normal rotation direction is obtained at time t11, switching is madeat time t12 to drive the cam in a normal rotation direction. In otherwords, normal rotation drive of the cam synchronizing with crankshaftrotation arises after time t12.

As described above, the eighth embodiment gradually increases the camrotation speed by imparting motor torque to the camshaft so as to drivethe cam to swing during a cam base circle slide after the beginning ofengine startup. As a result, the cam phase gradually increases togradually increase the camshaft rotary inertia force. When the camshaftrotary inertia force later reaches a predetermined value necessary fornormal rotation drive, normal rotation drive of the cam synchronizingwith crankshaft rotation arises. When the camshaft rotary inertia forceis gradually accumulated while the cam is driven to swing as describedabove, a predetermined value (peak torque) necessary for normal rotationdrive can be attained even using a motor with a low rating. Therefore,the eighth embodiment can provide lower motor resistance than theseventh embodiment, which has been described earlier.

Ninth Embodiment

A ninth embodiment of the present invention will now be described withreference to FIGS. 25 to 27.

The hardware shown in FIGS. 1 to 5 can be used as a system according tothe ninth embodiment.

Features of Ninth Embodiment

The eighth embodiment, which has been described earlier, graduallyincreases the cam swing range (phase) at engine startup to increase thecam rotation speed and camshaft rotary inertia force, and then switchesthe cam from the swing drive mode to the normal rotation drive mode. Inthe eighth embodiment, however, no motor torque is imparted to thecamshaft during a valve lift. This scheme is employed to reduce thepower consumption of the motor during a valve lift.

An engine startup request is not only generated in compliance with anacceleration request, which is based on a vehicle driver's acceleratoroperation, but also generated in compliance with a catalyst warm-uprequest, which is issued when the catalyst bed temperature is low. Ifthe catalyst bed temperature is not higher than a predetermined valuewhile the engine is stopped, the ECU 30 judges that an engine startuprequest is generated in accordance with a catalyst warm-up request. Thecatalyst bed temperature can be detected by the catalyst bed temperaturesensor 45 shown in FIG. 3. Further, if an accelerator pedal is depressedwhile the engine is stopped, the ECU 30 judges that an engine startuprequest is generated in accordance with an acceleration request. Adepressed accelerator pedal can be detected by the accelerator anglesensor 36 shown in FIG. 3.

When an engine startup request is generated in accordance with anacceleration request, it is necessary to start the engine in a shortperiod of time. To achieve engine startup in a short period of time, itis preferred that the cam is switched from the swing drive mode to thenormal rotation drive mode in a short period of time. The reason is thatthe normal rotation drive mode for the cam provides a larger time areaand higher intake performance than the swing drive mode.

When, on the other hand, an engine startup request is generated inaccordance with a catalyst warm-up request, there is no need to startthe engine in a short period of time unlike in the case of theaforementioned engine startup request based on an acceleration request.

However, if the accelerator angle is significantly small, it is notalways necessary to start the engine in a short period of time no matterwhen an engine startup request is generated in accordance with anacceleration request.

Under the above circumstances, the ninth embodiment determines whetheror not to impart motor torque to the camshaft during a valve lift inaccordance with the degree of requested acceleration indicated by theengine startup request. In other words, the ninth embodiment changes amotor assist pattern in accordance with the engine startup request.

More specifically, the degree of requested acceleration is small when anengine startup request is generated in accordance with a catalystwarm-up request. In this instance, therefore, no motor torque isimparted to the camshaft during a valve lift as indicated in FIGS. 25Ato 25C. FIGS. 25A to 25C show an example of motor torque that isimparted in the ninth embodiment when an engine startup request isgenerated in accordance with a catalyst warm-up request. Morespecifically, FIG. 25A shows a valve lift; FIG. 25B shows a motorangular velocity; and FIG. 25C shows a motor torque (control instructionvalue). The motor angular velocity correlates with (is proportional to)the camshaft rotation speed.

When an engine startup request based on a catalyst warm-up request isacquired, an engine startup sequence begins at time t20, which is shownin FIGS. 25A to 25C. As indicated in FIG. 25B, the motor angularvelocity is zero at time t20. During a cam base circle slide betweentime t20 and time t21 at which a valve lift for the first cylinder #1starts, motor torque is imparted to the camshaft. The motor angularvelocity and camshaft rotation speed then increase. During a subsequentvalve lift between time t21 and time t23, no motor torque is imparted tothe camshaft. Therefore, the spring reaction force oriented in adirection opposite the camshaft rotation direction reduces the motorangular velocity and camshaft rotation speed before the maximum lift isprovided at time t22. After time t22, the camshaft rotation directionreverses so that the spring reaction force oriented in the samedirection as the reversed camshaft rotation direction increases themotor angular velocity and camshaft rotation speed.

During a subsequent cam base circle slide between time t23 at which thevalve lift terminates and time t24 at which a valve lift for the fourthcylinder #4 starts, motor torque oriented in the same direction as thecamshaft rotation direction is imparted. As a result, the motor angularvelocity (absolute value) at time t24 is higher than the motor angularvelocity (absolute value) at time t21.

During a subsequent valve lift between time t24 and time t26, no motortorque is imparted to the camshaft as is the case with the intervalbetween time t21 and time t23. Therefore, the spring reaction forceoriented in a direction opposite the camshaft rotation direction reducesthe motor angular velocity and camshaft rotation speed before themaximum lift is provided at time t25. After time 25, the camshaftrotation direction reverses so that the spring reaction force orientedin the same direction as the camshaft rotation direction increases themotor angular velocity and camshaft rotation speed.

During a subsequent cam base circle slide after time t26 at which thevalve lift terminates, motor torque oriented in the same direction asthe camshaft rotation direction is imparted. As a result, the motorangular velocity and camshaft rotation speed for normal rotation driveare reached at time t27. Therefore, the motor torque is changed to atorque composed of friction torque only. After time t27, the cam isswitched to the normal rotation drive mode, and control is exercised tosynchronize the cam with the crankshaft. Consequently, the cam is drivenin a normal rotation direction to perform a valve lift for the firstcylinder #1 during the interval between time t28 and time t30. Thismakes it possible to perform ignition for the first cylinder #1.

On the other hand, when an engine startup request based on anacceleration request is acquired, motor torque is imparted to thecamshaft during a valve lift as shown in FIGS. 26A to 26C. FIGS. 26A to26C show an example of motor torque that is imparted in the ninthembodiment when an engine startup request is generated in accordancewith an acceleration request. More specifically, FIG. 26A shows a valvelift; FIG. 26B shows a motor angular velocity; and FIG. 26C shows amotor torque (control instruction value)

When an engine startup request based on an acceleration request isacquired, an engine startup sequence begins at time t40, which is shownin FIGS. 26A to 26C. As indicated in FIG. 26B, the motor angularvelocity is zero at time t40. During a cam base circle slide betweentime t40 and time t41 at which a valve lift for the fourth cylinder #4starts, motor torque is imparted to the camshaft. The motor angularvelocity and camshaft rotation speed then increase.

During a subsequent valve lift between time t41 and time t43, motortorque is also imparted to the camshaft unlike in the case shown inFIGS. 25A to 25C. More specifically, the same motor torque as for aperiod preceding time t41 is imparted during the interval between timet41 at which a valve lift starts and time t42 at which the maximum liftis provided, and motor torque oriented in an opposite direction isimparted during the interval between time t42 and time t43 at which thevalve lift terminates. As a result, the motor angular velocity (absolutevalue) at time t43 at which the valve lift terminates is higher than themotor angular velocity (absolute value) at time t41 at which the valvelift starts.

During a subsequent cam base circle slide after time t43 at which thevalve lift terminates, the same motor torque as for the interval betweentime t42 and time t43 is imparted. As a result, the motor angularvelocity and camshaft rotation speed for normal rotation drive arereached at time t44. Therefore, the motor torque is changed to a torquecomposed of friction torque only. The interval between time t40 and timet44 is shorter than the interval between time t20 and time t27, whichare shown in FIGS. 25A to 25C. In other words, the example shown inFIGS. 26A to 26C makes it possible to switch to the normal rotationdrive mode in a shorter period of time than the example shown in FIGS.25A to 25C.

After time t44, the cam is switched to the normal rotation drive mode,and control is exercised to synchronize the cam with the crankshaft.Consequently, a valve lift is performed for the first cylinder #1 duringthe interval between time t45 and time t47. This makes it possible toperform ignition for the first cylinder #1.

Details of Process Performed by Ninth Embodiment

FIG. 27 is a flowchart illustrating a routine that the ECU 30 executesin the ninth embodiment. The routine is started at predetermined timeintervals while the engine is stopped due, for instance, to the use ofan EV mode.

First of all, the routine shown in FIG. 27 judge whether an enginestartup request is generated performs (step 100). In step 100, if thecatalyst bed temperature is equal to or lower than the predeterminedvalue, it is judged that an engine startup request is generated inaccordance with a catalyst warm-up request. If, on the other hand, avehicle driver has operated an accelerator (stepped on the acceleratorpedal), it is judged that an engine startup request is generated inaccordance with an acceleration request. If it is judged in step 100that no engine startup request is generated, the routine terminates.

If it is judged in step 100 that an engine startup request is generated,the engine startup request is acquired (step 102). Next, it is judgewhether the degree of requested acceleration indicated by the enginestartup request acquired in step 102 is equal to or larger than apredetermined value (step 104). Step 104 is performed to judge whetherengine startup in a short period of time is requested. Morespecifically, this step is performed to judge whether the acceleratorangle is equal to or larger than a predetermined value.

If it is judged in step 104 that the degree of requested acceleration issmaller than the predetermined value in a situation, for instance, wherethe accelerator pedal is slightly stepped on or where catalyst warm-upis requested with the accelerator pedal insignificantly stepped on, itis concluded that engine startup in a short period of time is notrequested. In this instance, motor torque is imparted to the camshaftonly during a cam base circle slide (step 106). In step 106, motortorque control shown, for instance, in FIGS. 25A to 25C is exercised.

If, on the other hand, it is judged in step 104 that the degree ofrequested acceleration is equal to or more than the predetermined valuein a situation, for instance, where the accelerator pedal isconsiderably stepped on, it is concluded that engine startup in a shortperiod of time is requested. In other words, it is concluded that thecam needs to be driven in a normal rotation direction in a short periodof time. In this instance, motor torque is imparted to the camshaft notonly during a cam base circle slide but also during a valve lift (step108). In step 108, motor torque control shown, for instance, in FIGS.26A to 26C is exercised.

After completion of step 106 or 108, it is judge whether the camshaftrotary inertia force is equal to or more than a predetermined value(step 110). The predetermined value (that is, the peak torque)represents the camshaft rotary inertia force required for driving thecam in a normal rotation direction and is used as a reference value forjudging whether it is possible to switch the cam from the swing drivemode to the normal rotation drive mode. If it is judged in step 110 thatthe camshaft rotary inertia force is smaller than the predeterminedvalue, flow returns to step 110. If, on the other hand, it is judged instep 110 that the camshaft rotary inertia force is equal to or more thanthe predetermined value, the camshaft is placed in the normal rotationdrive mode and control for synchronizing the camshaft with the rotationof the crankshaft is exercised (step 112). Upon completion of step 112,the routine terminates.

As described above, when the degree of requested acceleration indicatedby the engine startup request is high, the ninth embodiment impartsmotor torque not only during a cam base circle slide but also during avalve lift. Since this allows the camshaft rotary inertia force toincrease in a short period of time, it is possible to switch from theswing drive mode to the normal rotation drive mode in a short period oftime. As a result, a high degree of requested acceleration can beachieved in compliance with a request. When, on the other hand, thedegree of requested acceleration indicated by the engine startup requestis low, the ninth embodiment imparts motor torque only during a cam basecircle slide. Since this causes the cam to be switched from the swingdrive mode to the normal rotation drive mode in a relatively long periodof time, the power consumption of the motor can be reduced.Consequently, the ninth embodiment can not only reduce the motor ratingbut also switch from the swing drive mode to the normal rotation drivemode with optimum timing according to the degree of requestedacceleration.

In the ninth embodiment, the “control means” according to the thirteenthaspect of the present invention is implemented when the ECU 30 performssteps 108, 110, and 112; the “startup request acquisition means”according to the fourteenth aspect of the present invention isimplemented when the ECU 30 performs step 102; the “control means”according to the fourteenth aspect of the present invention isimplemented when the ECU 30 performs steps 104, 106, and 108; the“judgment means” according to the fifteenth aspect of the presentinvention is implemented when the ECU 30 performs step 104; and the“control means” according to the fifteenth aspect of the presentinvention is implemented when the ECU 30 performs steps 106 and 108.

1. A variable valve mechanism control device for an internal combustionengine, comprising: a camshaft on which a cam is mounted to drive avalve that is biased by a valve spring; an electric motor whichrotationally drives the camshaft; and control means for exercising drivecontrol over the electric motor; wherein the control means controls therotary inertia force of the camshaft so as to be equal to or more than apredetermined value at the beginning of a valve lift so that the rotaryinertia force cancels the spring reaction force of the valve spring. 2.The variable valve mechanism control device according to claim 1,wherein the control means controls the rotational position of theelectric motor so that the rotation speed of the camshaft is decreasedby the spring reaction force exerted during the time interval betweenthe instant at which a valve lift starts and the instant at which themaximum lift position is reached, and that the rotation speed of thecamshaft is increased by the spring reaction force exerted during thetime interval between the instant at which the maximum lift position isreached and the instant at which the valve lift terminates.
 3. Thevariable valve mechanism control device according to claim 1, whereinthe control means employs the spring reaction force exerted during thetime interval between the instant at which the valve lift starts and theinstant at which the maximum lift position is reached as decelerationtorque for the rotary inertia force, while employing the spring reactionforce exerted during the time interval between the instant at which themaximum lift position is reached and the instant at which the valve liftterminates as acceleration torque for the rotary inertia force.
 4. Thevariable valve mechanism control device according to claim 1, wherein,when the rotary inertia force exerted at the end of the valve lift issmaller than the predetermined value, the control means requires duringa cam base circle slide to the electric motor to generate such torquethat causes said rotary inertia force to be equal to or more than thepredetermined value.
 5. The variable valve mechanism control deviceaccording to claim 1, wherein the control means inhibits the electricmotor to generate torque opposing the spring reaction force and requiresthe electric motor to generate only torque opposing the friction of thecam and valve during a valve lift.
 6. The variable valve mechanismcontrol device according to claim 1, further comprising: engine speedchange means which raises an engine speed to a value equal to or morethan a predetermined value when a requested engine output value is equalto or more than a predetermined value and the engine speed is in a lowrotation speed region where the engine speed is equal to or lower thanthe predetermined value.
 7. The variable valve mechanism control deviceaccording to claim 1, further comprising: an inertia force increasemember which is installed in a cam drive system having the camshaft andthe electric motor to increase the camshaft rotary inertia force;wherein the inertia force increase member adjusts the enlargement rangefor an actual operating angle in a low rotation speed region where anengine speed is equal to or lower than a predetermined value.
 8. Thevariable valve mechanism control device according to claim 1, furthercomprising: an inertia force change mechanism which can change thecamshaft rotary inertia force when the operating angle of the valve isto be changed within a low rotation speed region where an engine speedis equal to or lower than a predetermined value.
 9. The variable valvemechanism control device according to claim 1, wherein, when the cam isto be driven from a stopped state, the control means requires theelectric motor to generate such torque that causes the rotary inertiaforce to be equal to or more than a predetermined value during a cambase circle slide before the start of a valve lift.
 10. The variablevalve mechanism control device according to claim 1, wherein, when thecam is to be driven from a stopped state, the control means requires theelectric motor to generate such torque that causes the rotary inertiaforce to reach a predetermined initial value during a cam base circleslide before the start of a valve lift, and then requires the electricmotor to generate such torque that causes the rotary inertia force atthe end of the valve lift to reach a predetermined value greater thanthe predetermined initial value.
 11. The variable valve mechanismcontrol device according to claim 1, wherein, when the cam is to bedriven in a normal rotation direction, the control means changes therotation speed of the camshaft during a cam base circle slide inaccordance with an engine speed so that the rotation of the camshaftsynchronizes with the rotation of a crankshaft.
 12. A variable valvemechanism control device for an internal combustion engine, comprising:a camshaft on which a cam is mounted to drive a valve that is biased bya valve spring; an electric motor which rotationally drives thecamshaft; and control means for exercising drive control over theelectric motor; wherein the control means controls the rotationalposition of the electric motor so that the cam rotation speed during avalve lift is equal to or lower than the cam rotation speed during a cambase circle slide.
 13. The variable valve mechanism control deviceaccording to claim 1, wherein the control means increase the rotaryinertia force to a value equal to or more than a predetermined value byimparting torque of the electric motor during a cam base circle slide soas to swingingly drive the cam, and then synchronizes the rotation ofthe camshaft with the rotation of a crankshaft.
 14. The variable valvemechanism control device according to claim 13, further comprising:startup request acquisition means for acquiring a startup request forthe internal combustion engine; wherein the control means changes theperiod for swingingly driving the cam to increase the rotary inertiaforce in compliance with the startup request acquired by the startuprequest acquisition means.
 15. The variable valve mechanism controldevice according to claim 14, wherein the control means includesjudgment means for determining the degree of requested accelerationindicated by the startup request, applies the torque of the electricmotor only during a cam base circle slide if the degree of requestedacceleration is smaller than a predetermined value, and applies thetorque of the electric motor not only during a cam base circle slide butalso during a valve lift if the degree of requested acceleration isequal to or more than the predetermined value.
 16. A variable valvemechanism control device for an internal combustion engine, comprising:a camshaft on which a cam is mounted to drive a valve that is biased bya valve spring; an electric motor which rotationally drives thecamshaft; and a control unit for exercising drive control over theelectric motor; wherein the control unit controls the rotary inertiaforce of the camshaft so as to be equal to or more than a predeterminedvalue at the beginning of a valve lift so that the rotary inertia forcecancels the spring reaction force of the valve spring.
 17. A variablevalve mechanism control device for an internal combustion engine,comprising: a camshaft on which a cam is mounted to drive a valve thatis biased by a valve spring; an electric motor which rotationally drivesthe camshaft; and a control unit for exercising drive control over theelectric motor; wherein the control unit controls the rotationalposition of the electric motor so that the cam rotation speed during avalve lift is equal to or lower than the cam rotation speed during a cambase circle slide.